ES2382786B1 - METHOD AND VOLTAGE CONTROL SYSTEM OF AN ELECTRICAL GENERATION CENTER AND WIND FARM - Google Patents

Abstract

Method and voltage control system of a power generation plant and wind farm, whose method comprises estimating the equivalent voltage of the network (V {sub, Network}) from the electrical quantities measured at the connection point of the generation plant (V {sub, Sub}), P {sub, global}, Q {sub, global}, I {sub, global}, cos fi), and an equivalent model of the power grid to which connect the park; and generation from said calculated equivalent voltage (V {sub, Red}) of a setpoint (Q {sub, ref}) indicative of the reactive power to be produced by the power generation plant, so that the system calculates the setpoint of reactive applying a control method, and being all applicable in a wind farm.

Description

Method and voltage control system of a power generation plant and wind farm.

Object of the invention

The following invention, as expressed in the statement of the present specification, refers to a voltage control method of a power generation plant, having as its essential object the generation of reactive power according to the evolution of the voltage, so that it contributes to the stabilization of the network voltage.

A second object of the invention refers to a voltage control system of a power generation plant comprising said voltage control method.

A third object of the invention refers to a wind farm comprising said control system.

Scope

This method describes a method and a voltage control system of a power plant, being especially applicable in a power plant.

Background of the invention

With the increase in the degree of penetration of renewable power plants in the electricity grid, various auxiliary services, such as voltage and frequency control, are being demanded from these types of generators to ensure their correct integration into the network.

In this way, active and reactive power controls have been developed to contribute to frequency and voltage stabilization, respectively.

This type of generation plants are usually made up of low-power generation units (photovoltaic panels, wind turbines, etc. of the order of kW to 10 MW) in relation to conventional power plants (thermal, nuclear, etc.) that can reach up to GW order). The coordination and control of all the constituent generation units of the renewable generation plant, makes it essential that communication systems be available that send the necessary information to each of them.

Wind generation in particular is one of the forms of renewable generation that has increased more and more rapidly. These types of generating units have conventionally used two different strategies for voltage control in normal operation.

The first strategy has been to incorporate in the wind turbines voltage control terminals on the wind turbine. An example of this type of control is US Patent 6965174 B2.

This type of control is quick response and does not need additional substation control equipment, since wind turbines always incorporate controllers and voltage measurements in connection terminals.

However, it has the disadvantage that only local voltage is controlled, the value of which is not relevant for the power grid as long as it remains within the specified operating ranges. On the contrary, the voltage at the connection point of the park is not controlled and therefore may be subject to variations.

The second strategy has been to incorporate park controllers, which, based on the voltage measured at the connection point of the park, send instructions to the reactive power or power factor wind turbines. Examples of this type of control are patent application EP1433238 and part of what is described in patent document US7166928B2.

The disadvantage of this solution is that in order to get a quick response, it requires a sophisticated computer network that connects the park controller with the wind turbines.

On the other hand, associated to the delays that exist in the course from the moment the measurements are taken and the instructions in substation for the generation units are calculated until the generating units receive them and generate accordingly (digital and communication and communication delays response of the systems), oscillations of the voltage and the reactive generated can occur.

In some network regulation regulations, they specify the level of reactive power to be generated based on the voltage deviation, in many cases imposing a proportional voltage regulator as a requirement. They also specify the required response time of said regulator.

This type of control can lead to the appearance of additional voltage fluctuations depending on the type of network to which it is connected to the wind farm (usually with low short-circuit powers), the proportionality constant (or droop) required in the control, etc.

In the present invention, a voltage control method of a generation plant that solves the aforementioned drawbacks is proposed.

Description of the invention

In this report a voltage control method of a power generation plant is described, characterized by comprising the following steps:

-

estimation of the equivalent network voltage (VRed) from the electrical quantities measured at the connection point of the power generation plant (VSub, Pglobal, Qglobal, Iglobal, cos fi), and an equivalent model of the electricity grid to which the park is connected;

-

generation from said calculated equivalent voltage (VRed) of a setpoint (Qref) indicative of the reactive power to be produced by the power generation plant.

When generating the setpoint of reactive power from the network voltage (VRed), much more stable than the connection point voltage (VSub), especially in the case of weak networks, the control will be more stable than those of the state of the art, not being subject to the oscillations observed in said voltage of the connection point, and which consequently generate fluctuations in the reactive power setpoints. Thus, the voltage at the connection point of the power plant obtained by applying the method of the invention is more stable than those of the prior art.

In another aspect of the invention, the reactive power setpoint (Qref) is calculated from the equivalent network voltage (VRed) and has a value corresponding to the reactive power that the power generation plant must generate in a stationary way to comply a control law previously defined.

The fact that the setpoint of reactive power corresponds to that which must be generated by the power generation plant in the steady state, prevents the delays that exist in the course since the measurements are taken and the sub-station setpoints are calculated for the units of generation until the generating units receive them and generate accordingly (digital and communication delays and response of the systems), affect the controllability of the system.

In a first alternative of the invention, the control law defines the reactive power to be generated (Qref) as a function of the voltage at the connection point of the power generation plant (VSub) and a reference voltage (Vref).

According to the first alternative of the invention, the voltage at the connection point (VSub − Est) is calculated, which will be achieved stationary at the equivalent voltage of the network (VRed) and generating a reactive power equal to the setpoint (Qref) .

Said voltage control law, according to the first alternative of the invention, may be imposed by the network operator in charge of ensuring the stability of the electrical system and usually corresponds to a proportional control. In this case, the control law that defines the required response to the power generation plant includes in addition to the reference voltage for the voltage at the connection point (Vref), a constant (K) that relates the voltage at the point of connection (VSub) and the reactive power to be generated (Qref) by the power generation plant.

In a second alternative of the invention, the control law defines the voltage that must be reached stationary at the park connection point (Vref). In this way, the setpoint (Qr) corresponds to the reactive power that the power generation plant must generate in a stationary way to eliminate the steady state error between the setpoint voltage (Vref) and the measurement.

In another aspect of the invention, the control method further comprises the step of dynamically estimating the electrical model of the network from the electrical quantities measured at the connection point of the power generation plant (Vs, P, Q, I , cos fi).

In this way, changes in the electricity grid are detected (load shedding, disconnection of generation units, etc.) that affect the equivalent impedance of the network. Due to the fact that the network model is used in the voltage control of the present invention, the fact of detecting impedance modi fi cations makes it possible to minimize the error made in the calculation of the reactive power setpoints.

Said electrical model of the network consists of a resistor (R) and a reactance serle (X).

In another aspect of the invention records of several consecutive values of impedances of the network are kept, so that in case of sudden changes in the value of said impedance, parameters in the voltage control, such as the response time or the constant, are modified of proportionality (K), so that control stability is still guaranteed.

Another object of the invention is to provide a voltage control system of a power generation plant, said system comprising measuring means of electric variables at the connection point of the power generation plant and a control unit that calculates from The electrical variables are a reactive power setpoint (Qref) in which, in addition, the reactive setpoint is calculated by applying a control method as described above.

Another object of the invention is a wind farm characterized by comprising a control system as described above.

In order to complement the description that is going to be carried out below, and in order to help a better understanding of the characteristics of the invention, this descriptive report is accompanied by a set of drawings whose figures are illustrative and not limiting, The most characteristic details of the invention are shown.

Brief description of the designs

Figure 1. Shows the scheme of a distributed generation plant according to a preferred embodiment.

Figure 2. Shows the scheme of a proportional voltage regulator, according to the requirements of some network operators.

Figure 3. Shows the scheme of an integral proportional voltage regulator.

Figure 4. Shows the scheme of a voltage regulator according to a preferred embodiment.

Figure 5. Shows an equivalent circuit per phase of the power grid to which the power generation plant is connected.

Figure 6. Shows the control scheme according to a preferred embodiment.

Figure 7. Shows an iterative resolution method according to a preferred embodiment.

Figure 8. Shows an iterative resolution method according to a preferred embodiment.

Figure 9. Shows the evolution of the grid voltage and the power of a wind farm.

Figure 10. It shows the evolution of the reference and measured substation voltage and the reactive power measured in a wind farm, according to a conventional voltage control.

Figure 11. It shows the evolution of the reference and measured substation voltage and the reactive power measured in a wind farm, according to a voltage control of a preferred embodiment.

Figure 12. Shows the evolution of the reference and measured substation voltage and the reactive power measured in a wind farm, according to a voltage control of a preferred embodiment.

Description of a preferred embodiment

In view of the aforementioned figures and according to the numbering adopted, in Figure 1 the scheme of a distributed generation plant (for example, a wind farm) can be observed.

The distributed generation plant is composed of at least two. generation units (or wind turbines) 1, a park network 2, a central control unit 3, a transformer 4, a measurement unit 5 and a communication network 6.

Said generation plant is connected to the power grid 5 through a transformer 4 that adapts the voltage of the park network 2 or generation voltage level to the voltage of said power grid 7 or voltage level of the power grid. distribution or transportation, as appropriate.

The central control unit 3 receives information from the measurement unit 5 about the active and reactive power generated by the generation plant, the voltage level or the current (Pglobal, Qglobal, VSub), measured well on the side of the distributed generation plant 2, or on the side of the network to which the generation plant 7 is connected. This information is used by the central control unit to calculate and send setpoints to the reactive and active power generating units ( QI, PI) that respond to the voltage and frequency controls that may be required by the corresponding network operator.

In Figure 2 you can see the scheme of a proportional voltage regulator, as required by some network operators as the degree of penetration of renewable generation increases. Said regulator establishes a quantity of reactive to be generated (Q) by the power plant proportional to the voltage error (ΔV) between the measured voltage (VMed) and the reference voltage (Vref) at the point where it is to be carried out Tension control Being a proportional regulator does not eliminate the error in permanent voltage regime.

An alternative to the previous one is the integral proportional regulator (PI) shown in Figure 3. Said regulator in function of the voltage error (ΔV) establishes a quantity of reactive to be generated by the generation plant so that the error in state is eliminated stationary as long as the generation units are not saturated, that is, they have the capacity to generate all the reagent that is consigned.

However, the integral control is not the one demanded by the network operators, since it can cause oscillations of generation and consumption of reactive by generators that have this type of control active and are connected to the same point of the network or nearby each other, due to disparity in the time constants of the controllers that the different generation units have implemented or errors in the voltage measurements.

It is for this reason that most network operators require a proportional voltage regulator.

However, the proportional regulator can cause voltage fluctuations, depending on the proportional controller constant required and the short-circuit power, in addition to communication delays and digital delays and delays associated with the response of the generation systems of reactive available to the generation plant (generation units, capacitor banks, FACTS devices, etc.).

This is caused due to the fact that the control is carried out based exclusively on the voltage measured at the point of connection of the park to the grid, which is much more susceptible to variations due to changes in the reactive and active power generated by the generation plant. Therefore, since a change in voltage occurs until the central control detects it and generates the necessary reactive setpoints, the generation units may be at a reactive generation point that is opposite to the desired one, increasing the error tensile.

On the other hand, from the moment the voltage reaches the reference voltage, until the generation units are notified, they continue to generate reactive as if there was an error, thus making the control oscillating.

The objective of the present invention is to eliminate the oscillations in the tension before variations in the operating conditions, without resorting to more agile and therefore more expensive communication equipment and systems, so that a control system of voltage of characteristics superior to those of the state of the art.

As can be seen in Figure 4, in a preferred embodiment for the calculation of the reactive setpoint (Qref) in block 9, measurements are taken at the point of connection to the generated active power network (Pglobal), reactive power (Qglobal) and voltage (VSub).

The reference voltage (VSub − ref) appropriate to the point where the voltage control is desired is also used.

In a preferred embodiment said point corresponds to the point of the network to which the power generation plant is connected.

For the calculation of said reactive power reference (Qref), an equivalent model of the power grid to which the power generation plant is connected is also used in block 9.

In Figure 5 the equivalent circuit per phase used in a preferred embodiment corresponding to said network model can be seen. The voltage (VSub) represents the voltage at the point of connection to the power plant, while the voltage (VRed) represents the voltage of the network and its impedance is given by a real part (RRed) and an imaginary one (jXRed). Using the transformation of (Park), the system of equations in axes (dq) that governs the behavior of the represented circuit, for a three-phase system of tensions is as follows:

The use of said network equivalent is based on the assumption that the most abrupt changes in the substation voltage are directly related to changes in the network voltage (VRed).

The use of these expressions also requires knowledge of the network impedance (RRed) and (XRed). This impedance depends on the generation consumption ratio, which translates into variations in the value of (RRed) and (XRed) at all times and makes it difficult to use the previous expressions.

In a preferred embodiment, the constant network impedance is assumed, leaving the changes in the network reflected only in the equivalent network voltage. Said impedance can be evaluated from tests or be provided by the system operator.

Before detecting a change in the substation voltage (VSub), it is necessary to calculate the voltage of the network (VRed) that has caused this change. For this, in a preferred embodiment, the currents (Id) and (Iq) of the previous system of equations are calculated from the measures of active power (Pglobal), reactive power (Qglobal) and voltage (VSub) at the point of Mains connection (PCC), which, taking the substation voltage aligned with the axis (q), can be performed according to the following expressions:

In a first preferred embodiment, a control of the proportional type of characteristics similar to that of Figure 3 is proposed. However, the proposed control does not directly use the voltage measured at the connection point (VSub-med) for the calculation of the reactive reference , but the tension at that point corresponding to the steady state, as shown in Figure 6.

In said figure 6 the control scheme according to said first preferred embodiment can be seen. In it, based on the measurements taken at the network connection point (Pglobal, Qglobal, VSub), the voltage at the connection point corresponding to the steady state (VSub − Est) to be reached in block 8 is calculated In the new situation.

From the existing error (ΔV) between said calculated voltage (VSub − Est) and the reference voltage (VSub − Ref), the reactive supply to be generated is calculated from the proportionality constant required by the system operator The power generation plant.

For this, it is considered in a preferred embodiment that, since the transients are in a similar event relatively rapid, before a change in the substation voltage and until the new stationary situation is reached, the active power generated by the wind farm (PGlobal) It is not substantially modified. Therefore, the active power generated in the future steady state will correspond to the measurement at that moment. On the other hand, it is also considered that the grid voltage (VRed) is not substantially modified as a consequence of the substation voltage control, but that the variables that will have changed in the steady state will be the reactive power generated (QGoblal) and the Substation voltage (VSub) as a consequence.

In this way, the control system provides, before a change in the system variables, the reference reactive power value (Qref) related to the new stationary voltage value (VSub − Est). When this reactive setpoint value (Qref) is applied to the wind farm 10 as a reference, any oscillation will be avoided, since the control does not take into account what happened with the variables during the transitory. The problems derived from communication and response delays of the generation units are thus overcome.

In a preferred embodiment, the set of equations used in block 9 of Figure 6 for the calculation of the substation voltage (VSub) in the future steady state are the following:

For the resolution of the previous system of equations, in an preferred embodiment an iterative method is proposed as can be seen in Figure 7.

In block 11 a series of steps are carried out prior to the iterative process, in order to obtain the necessary variables for said process. These are:

-

Obtaining measures 12 of active power generated by the park (PGlobal), total reactive power generated (QGlobal) and voltage at the point of connection to the mains or at the point where you want to perform the voltage control (VSub) .

-

Calculation of current 13 at the point where it is desired to carry out the voltage control in axes (dq), (id − Sub) and (iq − Sub), from the measurements of active power (Pglobal), reactive power (Qglobal ) and voltage (VSub) at the grid connection point (PCC), which, taking said voltage aligned with the axis (q), according to the following expressions:

-

Calculation of the mains voltage 14 in axes (dq), (Vd − Red) and (Vq − Red), according to the equations that govern the behavior of the equivalent circuit per phase of the electrical network to which the park shown in Figure 4, that is:

Of the variables measured, calculated or estimated in block 11, the following are assumed constant throughout the iterative process:

-

The total generated power (Pglobal), which follows a slow dynamic. It is considered that in the event of a change in the network voltage and until the stationary is reached after said change, the variable that changes accordingly is the reactive power generated (Qglobal).

-

The network voltage calculated in axes (dq), (Vd − Network) and (Vq − Network). The generation or consumption of the reactive corresponding to the voltage control is assumed to have no influence on said mains voltage, but only on the substation voltage.

Once the calculations have been made in block 11, the iterative process 15. This process comprises the following steps:

-

Calculation in block 16 of the reactive powers (Qk) and (Qk) from the following expressions, where

ref Calc

superscript K identifies the iteration number:

-

Verification in block 17 that the calculated reactive power corresponds effectively to that corresponding to the steady state. For this, the difference between the reactive power calculated from the system currents and voltages (Qk) and the reference reactive power corresponding to

Calc

said tensions (Qk). This difference is called an error:

ref

In a preferred embodiment, a dimension is established that cannot be overcome by the error between the calculated reactive power and the reference reactive power, so that the result is considered as corresponding to the steady state:

If the error is greater than the set dimension, a new iteration starts. -Calculation in block 18 of a new reactive power (Qk) that is calculated as a linear combination of (Qk)

MedCalc

and (Qk) in order for the system to converge, as follows:

ref

K1 and K2 can be pre-set so that the number of iterations necessary to reach the final result is minimized.

-

Calculation in block 19 of the currents (ikq − Sub) and (ikd − Sub) that are set for the new reactive power (Qk) situation, taking into account that the active power remains constant, from the following

Med

expressions:

-

Calculation in block 20 of the voltages at the point where the control is carried out, based on the equations that model the behavior of the network to which the wind farm is connected and the previously calculated currents, taking into account that (Vd− Red) and (Vq − Red) do not change with respect to the previous step to the iterative process:

-

With the voltages and currents, within the iterative process 15, the reference reactive power and calculated reactive power are calculated again, and the iterative process is similarly continued.

If indeed in block 17 it is verified that

the iterative process with

In this block, the voltage corresponding to the steady state that will be reached as a result of the change in the grid voltage and when generating the reagent required for this new situation is calculated. Said axle tension (dq) responds to the following expression:

As can be seen in Figure 6, in a preferred embodiment said stationary voltage (VSub-Est) is used for the calculation of the error (ΔV) to which a gain (K) is applied for the calculation of the reactive power of reference.

In a second preferred embodiment, the system of equations solved in block 9 of Figure 4 is such that an equation is included that equals the reference voltage to the effective value of the voltage measured at the point at which the control is performed, thus imposing a null error in the steady state.

From the resolution of the system of equations a reactive power production (QCalc) is obtained that eliminates the error in the steady state and that will be the one emitted as a reactive setpoint (Qref) to perform the voltage control.

For the resolution of the previous system of equations, in an preferred embodiment an iterative method is proposed as can be seen in Figure 8.

In the previous step, relative to block 11, at the beginning of the iterative process, the calculations coincide with those previously explained for Figure 7, just as the hypotheses of the Iterative process coincide: the generated power (PGlobal) and the network voltage (Vd − Red) and (Vq − Red) remain constant from one step to another of the iteration process.

Once the previous calculations have been made in 11, the iterative process 15. This process includes the following steps:

-

Verification in block 22 that the calculated substation voltage (or measured in the case of the first iteration) and the reference substation voltage are approximately equal, that is, that the error between them is less than a given dimension.

If the error is greater than the set dimension, a new iteration starts. -Calculation in block 23 of the target substation voltage on the axis (q) (Vq), from the setpoint

q − Sub − Objective

of tension (Vref). For this, it is considered that the tension on the d axis does not change, but coincides with that of the previous iteration. That is to say:

From this voltage and the network model to which the park is connected, the current is also calculated in block 23, objective on the axis (d) associated with the generation of reactive, (ikd − Sub − Objective), according to the following expression:

It is considered that the current in the axis (q) remains constant.

-

From this current on the target axis (d) and voltage on the target axis (q), the associated reactive power target Qk is calculated in block 24

Objective.

-

Calculation in block 25 of the currents (ikq − Sub) and (ikd − Sub) that are set for the new reactive power (Qk) situation, taking into account that the active power remains constant, from the following

objective

expressions:

-

Calculation in block 26 of the voltages at the point where the control is carried out, based on the equations that model the behavior of the network to which the wind farm is connected and the previously calculated currents, taking into account that (Vd− Red) and (Vq − Red) do not change with respect to the previous step to the iterative process:

If indeed in block 22 it is verified that

iterative process 15 concludes and

in block 27 the reactive power reference (Qref) is generated, equalizing it to the target reactive power (Qk),

objective

thus achieving a reactive power reference that eliminates the voltage error in the future steady state, much faster than a conventional integral proportional controller (PI).

The blocks described above may correspond to different devices of which a control unit is constituted, or alternatively a calculation unit may be adjusted to perform the calculations described above, each block described being a step of said calculation.

In a preferred embodiment, a wind farm control unit is a programmable device configured to execute the method described above. Both iterative methods are simple to implement in digital substation control systems (PLC), and require reduced calculation times.

In a preferred embodiment, a wind farm control system comprises means for measuring electrical variables at the connection point of the power generation plant and said control unit.

In Figure 9 you can see the active power generated by a wind farm that has an installed capacity of 27 MW and the equivalent network voltage of the system. A rapid variation of active power is considered as well as certain noise in the mains voltage, to analyze the robustness of the control systems. In this generation situation, the response of different types of voltage controls is analyzed.

Figure 10 shows the evolution of the substation voltage (Vsub) and the reactive power (Qsub − real) generated by the wind farm with a conventional voltage control. The response required by the system operator is such that, given a voltage deviation (ΔV) of 4%, the wind turbines must generate all the reactive they are capable of, with the appropriate sign, and with a response speed of one second. It is verified that with this type of voltage control, a good response is not achieved, because due to the delays, the characteristics of the network, and the type of response required by the operator, the system becomes oscillating.

Figure 11 shows the evolution of the substation voltage (Vsub) and the reactive power generated by the wind farm (Qsub-real) with a voltage control according to the first embodiment of the invention. The response required by the system operator is such that, given a voltage deviation (ΔV) of 4%, the wind turbines must generate all the reactive they are capable of, with the appropriate sign, and with a response speed of one second. It is checked that with this type of voltage control, a fast and stable response is achieved, since from the first moment a reactive power setpoint is calculated and sent that is adequate for the steady state of the voltage. The oscillations that are observed are due to the weakness of the network to which the wind farm is connected and to the oscillations of active power generated and the voltage of the network. In addition, due to the characteristics of the required response, the steady state error is not eliminated.

Figure 12 shows the evolution of the substation voltage (Vsub) and the reactive power generated by the wind farm (Qsub-real) with a voltage control according to the second embodiment of the invention. In this case the requirement is to eliminate the steady state voltage error. It is verified that with this type of tension control, a fast and stable response is achieved which, in addition, while the reactive capacity of the wind turbines allows it, eliminates the error in steady state. The oscillations observed are motivated by the reasons stated above.

In a preferred embodiment, the value of the grid impedance (Rred) and (Xred) is dynamically estimated from the electrical quantities measured at the connection point of the wind farm (VSub, PGlobal, QGlobal, I, cos fi).

The estimation method is based on the resolution of a system of equations in steady state, which reflects the behavior of the network in three near moments in time (t1), (t2), (t3). For the execution of the estimation of the network it is assumed that in these instants the module of the network voltage (VRed), as well as the impedance of the network remain constant.

Said system of equations, with the electrical variables expressed in axes (dq) synchronized to the grid frequency and the axis q being aligned with the substation voltage (VSub), is as follows:

where the superscripts (t1), (t2), (t3) identify the Instances of time to which the equations correspond. The currents (id − Sub) and (iq − Sub), as well as the voltages (Vq − Sub) at each moment are obtained from the measurements made at the point of connection of the park to the network.

From the resolution of the previous system of equations, the values of the resistance (RRed) and the inductance (XRed) of the equivalent model of the network used for the voltage control object of this invention are obtained.

In a preferred embodiment, the cycle time for estimating the equivalent impedance of the network is substantially greater than that of voltage control.

In a preferred embodiment, registers of several consecutive values of impedances of the network are kept, so that in the event of sudden changes in the value of said impedance, parameters in the voltage control are modified so that the stability of the control is still guaranteed. In a preferred embodiment one of said parameters is the gain (K) of the control shown in Figure 6.

In a preferred embodiment, in the event of sudden changes in the value of the network impedance, the control system signals said event by means of an alarm.

Claims (12)

1. Voltage control method of a power generation plant, characterized by comprising the following steps:

-

estimation of the equivalent network voltage (VRed) from the electrical quantities measured at the connection point of the power generation plant (VSub, Pglobal, Qglobal, Iglobal, cos fi), and an equivalent model of the electricity grid to which the park is connected;

-

generation from said calculated equivalent voltage (VRed) of a setpoint (Qref) indicative of the reactive power to be produced by the power generation plant.

2.

The voltage control method of an electric power plant according to claim 1, characterized in that the reactive power setpoint (Qref) is calculated from the equivalent network voltage (VRed) and has a value corresponding to the reactive power that the power generation plant must generate in a stationary way to comply with a pre-established control law.

3.

Voltage control method of an electric power plant, according to claim 2, characterized in that the control law defines the reactive power to be generated (Qref) as a function of the voltage at the connection point of the power plant (VSub) and of a reference voltage (Vref).

Four.

Voltage control method of an electric power plant according to claim 3, characterized in that the voltage at the connection point (VSub-Est) is calculated which will be reached stationary at the equivalent voltage of the network and generating a power reactive equal to the setpoint (Qref).

5.

Voltage control method of an electric power plant according to claim 3, characterized in that the control law is defined by a reference voltage for the voltage at the connection point (Vref) and a constant (K) that relates the voltage at the connection point (VSub) and the reactive power to be generated (Qref).

6.

A voltage control method of an electric power plant according to claim 2, characterized in that the control law defines the voltage that must be reached stationary at the park connection point (Vref).

7.

Voltage control method of a power generation plant, according to any of the preceding claims, characterized in that said method further comprises the step of dynamically estimating the network model from the electrical quantities measured at the point of connection of the plant of electricity generation (Vs, P, Q, I, cos fi).

8.

A voltage control method of a power generation plant according to claim 7, characterized in that said electrical model of the network consists of a resistor (R) and a series reactance (X).

9.

A voltage control method of a power generation plant according to claim 7, characterized in that records of several consecutive impedance values of the network are kept, so that in the event of sudden changes in the value of said impedance, parameters are modified in the tension control so that the stability of the control is still guaranteed.

10.

Voltage control system of a power generation plant, which comprises means for measuring electrical variables at the connection point of the power generation plant and a control unit that calculates a reactive power setpoint from the electrical variables ( Qref), characterized in that the reactive setpoint is calculated by applying a control method according to any one of claims 1 to 9.

11. Wind farm, characterized by comprising a control system according to claim 10. SPANISH OFFICE OF THE PATENTS AND BRAND Application no .: 200900729 SPAIN Date of submission of the application: 03.17.2009 Priority Date: REPORT ON THE STATE OF THE TECHNIQUE 51 Int. Cl.: See Additional Sheet RELEVANT DOCUMENTS

Category

56 Documents cited Claims Affected

Y

 (LARS HELLE) 04/10/2007 "Modeling and Comparison of PowerConverters for Doubly Fed Induction Generators in Wind Turbines", URL: http://vbn.aau.dk/files/14466775/final_thesis_lars_helle 1-4,6,10-11

Y

EN 2158116 T3 (ELECTRIC POWER RES INST) 01/09/2001, column 2, lines 5 - 11; column 4, lines 13-49; column 6, lines 1-17. 1-4,6,10-11

TO

 (FERNANDO SANTODOMINGO FLAMES); MADRID, September 2006; "Device to withstand voltage dips and reactive compensation in wind generators"; URL: http://www.iit.upcomillas.es/pfc/resumenes/44fed25bdc85d.pdf 3

Category of the documents cited X: of particular relevance Y: of particular relevance combined with other / s of the same category A: reflects the state of the art O: refers to unwritten disclosure P: published between the priority date and the date of priority submission of the application E: previous document, but published after the date of submission of the application

This report has been prepared • for all claims • for claims no:

Date of realization of the report 30.05.2012

Examiner R. Molinera de Diego Page 1/5

REPORT OF THE STATE OF THE TECHNIQUE Application number: 200900729 CLASSIFICATION OBJECT OF THE APPLICATION F03D7 / 02 (2006.01) F03D9 / 00 (2006.01) H02J3 / 18 (2006.01) Minimum documentation sought (classification system followed by classification symbols) F03D, H02J Electronic databases consulted during the search (name of the database and, if possible, terms of search used) INVENTIONS, EPODOC State of the Art Report Page 2/5  WRITTEN OPINION Application number: 200900729 Date of Completion of Written Opinion: 30.05.2012 Statement

Novelty (Art. 6.1 LP 11/1986)

Claims 1-11 Claims IF NOT

Inventive activity (Art. 8.1 LP11 / 1986)

Claims 5,7-9 Claims 1-4,6,10-11 IF NOT

The application is considered to comply with the industrial application requirement. This requirement was evaluated during the formal and technical examination phase of the application (Article 31.2 Law 11/1986).  Opinion Base.- This opinion has been made on the basis of the patent application as published. State of the Art Report Page 3/5  WRITTEN OPINION Application number: 200900729 1. Documents considered.- The documents belonging to the state of the art taken into consideration for the realization of this opinion are listed below.

Document

Publication or Identification Number publication date

D01

(LARS HELLE) 04/10/2007 "Modeling and Comparison of PowerConverters for Doubly Fed Induction Generators in Wind Turbines", URL: http://vbn.aau.dk/files/14466775/final_thesis_lars_helle

D02

ES 2158116 T3 (ELECTRIC POWER RES INST) 01.09.2001

D03

(FERNANDO SANTODOMINGO FLAMES); MADRID, September 2006; "Device to withstand voltage dips and reactive compensation in wind generators"; URL: http://www.iit.upcomillas.es/pfc/resumenes/44fed25bdc85d.pdf

2. Statement motivated according to articles 29.6 and 29.7 of the Regulations for the execution of Law 11/1986, of March 20, on Patents on novelty and inventive activity; quotes and explanations in support of this statement Of all the documents found, document D1 is considered the closest to the state of the art, from now on it will be named as D1, and document ES 2158116 T3 will be named as D2. The claims of the application are then compared with these documents.  First claim: Document D1 discloses a voltage control method of a power generation plant comprising the Next steps: -estimulation of the equivalent voltage; -generation from said calculated equivalent voltage of a setpoint indicative of the reactive power to be produced by The power generation plant. The modeling of the electrical network to which the park is connected is something belonging to common knowledge, through for example an ideal voltage source in series with an impedance that limits the short-circuit power at the point PCC Therefore, the main difference of document D1 with claim one is: Document D1 does not specify that the equivalent voltage corresponds to the network from the measured electrical quantities at the connection point of the power generation plant. However, these characteristics have already been used to control the power flow of the transmission line in the document D2 (see column 4, lines 9-33); also for an expert in the field combining these two documents does not It would involve inventive activity. Therefore, the first claim does not appear to involve inventive activity, as set forth in Article 8 of Law 11/86 of the Spanish Patent and Trademark Law.  Second claim: Document D2 discloses that the setpoint of the reactive power is calculated from the equivalent mains voltage and has a value that corresponds to the reactive power that the power generation plant must generate stationary to comply with a pre-established control law (see column 4, lines 45-49). Therefore, it seems that this second claim does not imply inventive activity either.  Third claim: The fact of defining the reactive power to be generated based on the voltage at the connection point of the power generation plant and a reference voltage does not seem to imply inventive activity, since they have been found in the state of the Technical documents that disseminate this feature, an example in the END OF CAREER PROJECT "Device to withstand voltage dips and reactive compensation in wind generators" of Dept. 2006 (http://www.iit.upcomillas.es/pfc/ summaries / 44fed25bdc85d.pdf), in which in section 4.3.1 the system grid connection point is modeled using a voltage wave product of other 2 voltages, a variable with the value of the mains voltage value and another which could be equivalent to that of the reference drafted in the present claim. Therefore, this claim does not seem to imply inventive activity. Claims fourth: It does not appear to contain such a characteristic that it seems to imply inventive activity. State of the Art Report Page 4/5  WRITTEN OPINION Application number: 200900729  Fifth claim: A defined control law has not been found in the state of the art through a reference voltage for the voltage at the PCC (Vref) and a constant K that relates the voltage at the connection point (Vsub) and the reactive power to generate. Therefore, this claim seems to imply inventive activity.  Claim 6: Document D1 defines the voltage to be reached at the connection point of the park (see section 3.2.1 Reference voltage generation). Therefore, this claim does not seem to imply inventive activity.  Seventh claim: The characteristic of dynamically estimating the network model from the electrical quantities measured at the point of connection of the power generation plant as another step in the method of analysis has not been found in the documents studied in the prior art. voltage control of a power generation plant; therefore it seems that it would not be obvious for a person skilled in the art to integrate this step into this type of procedure. Therefore, it seems that this claim involves inventive activity.  Eighth and ninth claims: These claims to depend on the seventh also seem to imply inventive activity.  Tenth claim: Any of the documents cited implicitly comprise means for measuring electrical variables at the point of PCC connection and a control unit that calculates a reactive power setpoint, being able to apply the claimed control method. Therefore, it seems that this claim does not imply inventive activity.  Eleventh Claim: There are many wind farms in the world capable of understanding a control system as claimed in the tenth claim. Therefore, it also does not seem to imply inventive activity. As indicated in article 5.2.c of Regulation 2245/1986 on the execution of the Patent Law, and in order to obtain a better understanding of the invention, it is suggested that in the later stages of the procedure a description be included in the description indication of documents D1 and D2, commenting on the most important contribution made to the state of the art. Said indication cannot extend the object of the invention, as originally presented. State of the Art Report Page 5/5